WASHINGTON — The Supreme Court's most conservative justices and its crucial swing voter sharply questioned the government's right to force people to buy health insurance on Tuesday, leaving the centerpiece of President Barack Obama's signature achievement in doubt.

Immediately and throughout the extraordinary two-hour hearing on the second day of oral arguments on the federal health care law, the justices raised scenarios that amounted to a big what if.

If Congress can impose an "individual mandate" for health insurance, could it compel Americans to purchase cellphones, eat broccoli or obtain burial insurance?

"You don't know if you're going to need a heart transplant or if you ever will. So, there's a market there. In some extent, we all participate in it," Chief Justice John Roberts said. "So, can the government require you to buy a cellphone because that would facilitate responding when you need emergency services? You can just dial 911 no matter where you are."

Justice Antonin Scalia picked up the thread. "Everybody has to buy food sooner or later, so you define the market as food, therefore, everybody is in the market; therefore, you can make people buy broccoli," he said, adding, "If the government can do this, what else can it not do?"

Solicitor General Donald Verrilli countered each time, saying that health insurance was a distinct market and that Congress had a right to regulate it under the commerce clause and its taxing authority. Most Americans who do not have insurance after the mandate takes effect in 2014 would have to pay a penalty that would rise to $695 annually in 2016.

The mandate is the key point of the overall challenge before the court, and the arguments on Tuesday carried an air that history was in the making. In the rapt audience were members of Congress and the Obama administration, including Attorney General Eric Holder and Health and Human Services Secretary Kathleen Sebelius.

With no decision expected until late June, both sides will have weeks to pound well-worn talking points. Pundits already were gaming the outcome.

Verrilli had a shaky performance, evident in almost the first words he spoke, followed by a gulp of water. "The Affordable Care Act addresses a fundamental and enduring problem in our health care system and our economy," he insisted.

His counterpart, Paul Clement, who is representing Florida and 25 other states challenging the law, was forceful and consistent, and argued that the mandate forces people to buy something they might not want.

"The mandate represents an unprecedented effort by Congress to compel individuals to enter commerce," Clement said.

Oral arguments are only part of a case, and justices may present a viewpoint for the sake of argument. Democrats held out hope the justices will make a deep review of the issues.

Obama and his allies are banking on precedent in which the court has largely backed Congress' ability to regulate commerce.

"I look back into history, and I see it seems pretty clear that if there are substantial effects on interstate commerce, Congress can act," said liberal Justice Stephen Breyer, invoking an old case in which the court found Congress could regulate wheat production and a recent one covering home-grown marijuana.

"Is this commerce? Well, it seems to me more commerce than marijuana," Breyer said.

Still, skepticism from the bench was abundant. Most worrisome for defenders of the law was Justice Anthony Kennedy joining the sharp questioning. Kennedy, appointed by Ronald Reagan, is often a swing vote in big cases.

At one point he said the mandate "changes the relationship of the federal government to the individual in a very fundamental way."

It raised the distinct possibility that the hard-to-read Kennedy will join Roberts, Scalia and the two other conservatives, Samuel Alito and Clarence Thomas, in striking down the mandate. The four liberal justices — Breyer, Ruth Bader Ginsburg, Sonia Sotomayor and Elena Kagan — signaled their support for the mandate.

Thomas was the only justice who did not speak, but he reliably votes with the conservatives.

A 5-4 decision has always been a possibility, reflecting the ideological divide on the court. But an open question is which side will win over Kennedy.

Despite strong clues early on, he concluded his remarks by saying that the health care issue is unique and that "most questions in life are matters of degree."

Kennedy said the young and uninsured are affecting insurance rates and medical care costs "in a way that is not true in other industries" — effectively taking the Obama administration's view.

"It gave me pause," Nebraska Attorney General Jon Bruning said in an interview afterward. "I think he's very thoughtful. I think all the justices are trying to be very thoughtful about this case and I'm hopeful he'll do the right thing."

Florida Attorney General Pam Bondi said she is confident the court would discard the individual mandate. At a news conference with Republican members of Congress, she deemed the mandate "a government overreach like we have never seen before in our history."

U.S. Sen. Marco Rubio, R-Fla., nodded to the congressional fight that would ensue if the mandate is ruled unconstitutional. "I hope that I can be a part of an effort here, to not just vote to repeal Obamacare, but to replace it," he said.

Democrats were far less upbeat, offering what seemed like token optimism that the law would be upheld. Senate Majority Leader Harry Reid, D-Nev., pointedly challenged CNN legal analyst Jeffrey Toobin's contention that the hearing was a "train wreck" for Obama and the mandate would be found unconstitutional.

If the mandate is on the rocks, today's final day of arguments becomes critical. The arguments will deal with whether parts of the law — some of which have bipartisan support — can survive. The court also will hear arguments about whether the law's expansion of Medicaid is constitutional.

Outside the court, another day of boisterous demonstrations ensued with hundreds of people carrying signs for and against the law. "The mandate is needed because it gives teeth to the legislation," said Cedric Bright, a physician from North Carolina.

But the opposition was much larger and organized. "They make you buy health care, what's next? They going to make you buy broccoli?" said Joe Bodick, 51, echoing almost word for word what was said inside.

Bodick was part of a bus caravan from Pittsburgh that joined hundreds of other demonstrators in a rally organized by the conservative group Americans for Prosperity.

The court's decision this summer could instantly change the dynamics of the presidential race. The mandate was once an idea embraced by conservatives in opposing the last Democratic attempt at health care reform, during the Bill Clinton era, and is part of the plan passed in Massachusetts when Republican presidential front-runner Mitt Romney was governor — a point Verrilli made in his closing remarks.

Alex Leary can be reached at leary@tampabay.com. Follow him on Twitter @learyreports.

Chief justice grills solicitor general on purchase of health insurance

Chief Justice John Roberts: That, it seems to me, is — and it's a passage in your reply brief that I didn't quite grasp. It's the same point. You say health insurance is not purchased for its own sake, like a car or broccoli; it is a means of financing health care consumption and covering universal risks. Well, a car or broccoli aren't purchased for their own sake, either. They're purchased for the sake of transportation or, in broccoli, covering the need for food.

Solicitor General Donald Verrilli: No —

Roberts: I don't understand that distinction.

Verrilli: The difference, Mr. Chief Justice, is that health insurance is the means of payment for health care, and broccoli is —

Roberts: Well, now that's a significant — I'm sorry.

Verrilli: And broccoli is not the means of payment for anything else. And an automobile is not —

Roberts: It's the means of satisfying a basic human need —

Verrilli: But —

Roberts: — Just as insurance is the means of satisfying —

Verrilli: But I do think that's the difference between existing commerce, activity in the market already occurring — the people in the health care market purchasing, obtaining health care services — and the creation of commerce. And the principle that we're advocating here under the commerce clause does not take the step of justifying the creation of commerce. … This is a regulation of existing commerce.

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